A polyimide, known as Kapton, and a fluorinated ethylene propylene, known as Teflon-FEP, are two polymers that transmit visible radiation when used as thin sheets. These materials are presently used in both ground and space applications.
The use of these materials in space as thermal control surfaces, encapsulants for solar cells, reflectors for concentrator arrays, and solar sail material introduces the problem of spacecraft charging. Electrical charge buildup on external spacecraft insulating surfaces can be dissipated by the use of thin conducting films on the insulator. The application of these films can be costly. The films alter the optical properties of the materials, add weight, and create new problems, such as stability of the coating's optical properties when exposed to space environments.
Kapton coated on one side with 0.1 .mu.m of aluminum has been proposed for solar sail, solar concentrators and reflectors in space. However, untextured Kapton has a sheet resistance of 10.sup.18 ohms/square. This is an unsatisfactorily high value when used in a space application where charging phenomena may be present.
A 100 A thick coating of chrome has been deposited on the Kapton surface in an attempt to solve this problem. The chrome coating lowers the sheet resistance to less than 10.sup.5 ohms/square, and it provides a thermal emittance of 0.40 so that the material can operate up to 0.3 A.U.(10 suns). However, the coating process is expensive, and the coating adds an undesirable weight penalty to the material. Also, problems arise because the chrome does not adhere well to the smooth Kapton surface.
Surfaces of materials have been bombarded in the past by ions of various materials. By way of example, Cohen et al U.S. Pat. No. 3,699,334 describes an apparatus which provides for polishing a refractory dielectric material using an argon ion beam. U.S. Pat. No. 3,900,636 to Curry et al discloses the use of ion bombardment to improve the cutting edge of a razor blade and to improve adhesion properties. U.S. Pat. No. 3,959,303 to Feneberg et al describes a method of treatment of a silicone elastomer using an ion beam to destroy selected layers. Marchand et al U.S. Pat. No. 4,115,303 is directed to a method of making semipermeable membranes from a polymer using radiation, such as an ion beam.